The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Moving Picture Experts Group (MPEG) and Video Coding Experts Group (VCEG) together stepped ahead of the existing MPEG-4 Part 2 and H.263 standard methods to develop a better and more excellent video compression technology. The new standard is called H.264/AVC (Advanced Video Coding) and was released simultaneously as MPEG-4 Part 10 AVC and ITU-T Recommendation H.264.
H.264/AVC (hereinafter referred to as ‘H.264’) uses a spatial predictive coding method, which is different from prior international video coding standards such as MPEG-1, MPEG-2, MPEG-4 Part2 Visual and the like. Conventional methods use “intra prediction” for coefficients transformed in Discrete Cosine Transform Domain (or DCT Transform Domain) to seek higher encoding efficiency resulting in degradation of the subjective video quality at low band transmission bit rates. However, H.264 adopts the method of encoding based on a spatial intra prediction in a spatial domain rather than in a transform domain.
In the aspect of the encoder to consider such encoding by the spatial intra prediction, information on the current block to be coded is predicted from information of an already encoded and reconstructed previous block, and encoding is performed only on the difference information between the outstanding actual block to be coded and the predicted block, and the encoded difference information is transmitted to a decoder. Then, the encoder may transmit parameters needed for prediction of the block to the decoder, or the encoder and decoder may be synchronized, so that they share the needed parameters for the decoder to predict the block. As for the decoder, the block information to be currently decoded is predicted by using already decoded and reconstructed adjacent block information and then added to the difference information transmitted from the encoder, which reconstructs the desired composition information. Then, again, if the parameters needed for the prediction are transmitted from the decoder, the corresponding parameters are decoded and used for prediction.
Intra predictions according to the H.264 standard are an intra—4×4 prediction, intra—8×8 prediction, intra—16×16 prediction, and the like, each including a plurality of prediction modes.
In the case of intra—4×4 prediction as shown in FIG. 1, the positions and predictive directivity of the adjacent pixels are considered to appoint nine prediction modes including a vertical mode (mode 0), horizontal mode (mode 1), direct current (DC) mode, diagonal down-left mode (mode 3), diagonal down-right mode (mode 4), vertical-right mode (mode 5), horizontal-down mode (mode 6), vertical-left mode (mode 7) and horizontal-up mode (mode 8).
In addition, in the case of intra—16×16 prediction as shown in FIG. 2, there are four prediction modes appointed including a vertical mode (mode 0), horizontal mode (mode 1), DC mode (mode 2) and plane mode (mode 3). The intra—8×8 prediction also has four modes similar to those of the intra—16×16 prediction.
Referring to FIGS. 1 and 2, the adjacent pixels for use in the prediction are limited to the pixels located at left and upper sides, because only the pixels reconstructed after the decoding can be used for the prediction. The encoder encodes blocks from the left to the right and from the upper side to the lower side according to the encoding order and sequentially transmits bitstreams resulting from compressing the blocks to the decoder. Therefore, reconstructed pixels exist at the left side and the upper side of the block to be currently encoded.
However, such a limitation of the pixels available for intra prediction to the left side and the upper side of the current block hinders an effective reduction of the spatial redundancy in the intra prediction mode, which is a primary cause of degrading the compression efficiency.
Further, the operation in unison between the inter prediction encoding and inter prediction decoding makes it difficult to expect an enhanced efficiency of the inter prediction decoding from the already deteriorated compression efficiency of the inter prediction encoding.